The subject matter described herein relates generally to methods and systems for wind turbines, and more particularly, to methods and systems for operating a wind turbine in noise reduced operation modes in an efficient manner.
Energy generated from wind, for example, through the use of large scale wind turbines has experienced rapid growth in recent years. Source of this growth may be the numerous environmental, technical and economic benefits related to wind generated energy production. Wind energy is widely available, renewable and reduces the production of greenhouse gases by diminishing the need of fossil fuels as energy source. Furthermore, improvements in design, manufacturing technologies, materials and power electronic devices of wind turbines has and will in the future continue to decrease production costs of wind turbines while increasing their energy production capabilities and efficiencies.
At least some known wind turbines include a tower and a nacelle mounted on the tower. A rotor is rotatably mounted to the nacelle and is coupled to a generator by a shaft. A plurality of blades extend from the rotor. The blades are oriented such that wind passing over the blades turns the rotor and rotates the shaft, thereby driving the generators to generate electricity.
In general, during operation wind turbines generate acoustic emissions in the form of audible noise measured in decibels (dB). Such noise may be of a mechanical or aerodynamic origin. Often, local regulatory levels may limit the allowable noise emission levels of a wind turbine or a wind turbine installation including a plurality of wind turbines (i.e., a wind park), especially, in cases where the wind turbine or wind park operates close to or in a densely populated area.
Generally, the noise from mechanical origin, which is caused by gears and bearings, has been reduced considerably over the past years, for instance by proper sound insulation and is therefore becoming less of a concern. However, in order to further reduce wind turbine noise, focus is now placed on reducing the aerodynamic noise produced by wind turbines.
Normally, aerodynamic noise is produced by the rotational movement of the rotor blades through air, for instance by the tip vortex noise that forms in the noise generation process on the outer part of the wind turbine blades. Reducing noise, which originates from the aerodynamic effects of a wind turbine, may be achieved, for instance, by optimizing the blade design (e.g., airfoil shape and materials used).
However, since noise generation has not yet been fully eliminated during the operation of a wind turbine, sound power management (SPM) of wind turbines has become a significant criterion, for instance, for site planning permission and acceptance of wind turbines while new projects are developed. To meet local regulatory levels of noise emission individual wind turbines or wind parks may also be operated partly (e.g., by night), or continuously in noise reduced operation (NRO) modes.
Typically, NRO modes and SPM schemes include predetermined set points of wind turbine parameters that generally determine the rotor speed and thus affect tip speed. For example, changing the pitch angle set point of one or more rotor blades of a wind turbine may change the rotor speed. Usually, simulation tools are used to produce values for the aforementioned set points.
To achieve certain noise emission levels NRO modes and SPM schemes of operation of wind turbines usually reduce the rotor speed. In general, this reduction in rotor speed implies that wind turbines generate electric power below their maximum possible power generation capacity at the present site conditions (especially wind speed). This results in considerable losses in annual energy production (AEP). However, such losses are often the compromise to get permission by local authorities for the wind turbine installation. On that account, it will be appreciated that in order to maximize AEP yields of wind turbines functioning in NRO modes and/or with SPM schemes the maximum capacity of a wind turbine for generating electric power and operating within such modes and/or schemes should be approached.
Hence, the subject matter described herein pertains to methods and systems that enable the aforementioned optimization of NRO modes and SPM schemes, which ensures that wind turbines extract the maximum amount of power from wind energy when operating under specific noise emission constraints.